The present invention relates generally to the mining of petroleum hydrocarbons from petroleum bearing formations. More particularly, this invention concerns the hydraulic mining of bitumen from tar sand formations that are either found too deep or of insufficient thickness to be mined economically by surface mining techniques. 2. The Background Art.
Petroleum is generally recovered by penetrating reservoirs with wells. When a well is drilled, the petroleum either flows to the surface by means of natural pressure or by pumping. However, there are many reservoirs which contain petroleum that is too viscous to be produced by conventional methods. Under these circumstances, different methods of extraction must be used.
One of the most viscous petroleum deposits is in tar sand deposits that are commonly found in the Western United States, Western Canada and Venezuela. These tar sand deposits contain significant amounts of bituminous petroleum. However, conventional well drilling techniques are ineffective in recovering bitumen from tar sands.
As a result, other methods of recovering bitumen from tar sands have been developed. One of the earliest methods used for recovering bitumen was surface mining. Surface mining is the process of removing the overburden from the surface so that the tar sands can be removed from an open pit. The overburden is typically removed by large-scale mining equipment.
Once the tar sands deposits are reached, the tar sand material is recovered by mechanical means and removed for later processing and extraction of the bitumen. Standard processing methods utilize hot water with or without hydrocarbon diluents or chemical additives to decrease the viscosity of the bitumen and separate it from the inorganic tar sand solids. Once the bitumen is separated from the tar sand the bitumen, being less dense than water, will rise to the surface of the water from which it is easily separated. The bitumen depleted sand material sinks in the water by the force of gravity.
As is well known in the art, there are a host of disadvantages with surface mining methods. First, surface mining is not economical in many cases. Surface mining is generally limited to areas in which the overburden is minimal and the tar sand formation is relatively thick so that efficient and economic removal of the tar sand is possible. As the ratio of overburden to tar sand increases, surface mining becomes less economic. Furthermore, surface mining creates significant expense associated with reclaiming the mined region and disposing of tailings that result from the processing and extraction of the bitumen. Unfortunately, most tar sand is at such a depth that it is not economic to remove the tar sand through surface mining. Where the overburden is too thick for economic removal through surface mining techniques, other mining methods must be used.
In an attempt to avoid the disadvantages associated with surface mining, other methods of bitumen recovery have been developed. One primary method is known as in-situ processing. In-situ processing methods separate the bitumen from the tar sand formation within the formation such that only the bitumen is pumped to the surface. Under these methods the bitumen depleted or lean sand material remains in the mined cavity to prevent subsidence.
Most in-situ methods generally begin by drilling a borehole through the overburden and completely through to the bottom of the tar sand formation. Once a borehole is drilled, the mining apparatus is inserted and the mining operation is begun. The mining operation typically begins by delivering heated jets of water into the tar sand formation. This process causes the formation to liquify into a slurry consisting of sand, water and bitumen.
Most in-situ methods do not pump the slurry material to the surface for processing. Rather, in-situ methods attempt to process and separate the bitumen from the tar sand formation in the mining cavity directly, then pump only the bitumen to the surface. The sand and other materials remain in the ground.
There are a variety of in-situ methods that have evolved in the art. One method known as a thermal method typically injects hot water or steam into the formation causing the bitumen to separate from the sand particles. Hot water is pumped into the borehole and delivered at a high velocity into the formation thereby causing the formation to erode and form a cavity. The thermal energy in the hot water raises the temperature of the formation thereby assisting in the erosion process and the separation of bitumen from the sand material. The bitumen tends to float to the surface of the heated water, which accumulates in the cavity. The bitumen then is pumped out and the remainder of the slurry material remains in the cavity.
Methods that solely rely on heat to erode the formation and cause the separation of the bitumen are generally regarded as inefficient. The size of a cavity in which effective bitumen/sand separation can be achieved is limited. As a result, the cost per unit of the bitumen recovered is very high.
While the use of solvent and chemical additives may make the erosion and separation processes more efficient, thereby reducing the costs for bitumen removal, these savings are offset by the added costs of the solvent and chemical additives as well as added processing steps. While some of the solvents or chemicals can be recycled and reused, there are additional costs associated with recycling. Furthermore, recycling is not perfectly efficient as some solvents or chemicals are lost and must be replaced.
Many in-situ methods also require the use of gases to maintain pressure within a mining cavity. As is well known in the art, when an underground cavity is mined there is always a danger that the overburden will collapse into the cavity. As a result, methods have been developed to prevent such a collapse. Unfortunately many of these methods require that a gas be introduced into the cavity at sufficient pressure to prevent the overburden from collapsing. Any time gas is used, there are additional risks and dangers associated with the containment of said gas or the possibility of explosion.
A typical example of in-situ methods is disclosed in U.S. Pat. No. 4,406,499 issued Yildirim (hereinafter referred to as "Yildirim"). Yildirim discloses a method that requires the drilling of a borehole through the overburden to the bottom of a tar sand deposit. A water jet means is inserted to the bottom of the deposit. The water is injected into the tar sand in order to create a slurry in the bottom of the cavity. The water jets are raised through the tar sand thereby filling the cavity with a slurry material until the top of the tar sand formation is reached.
Once the top is reached, the water jet apparatus is removed and a separate apparatus comprising a system of small pipes is introduced to the bottom of the slurry mixture. Hot water is introduced into the slurry through the pipes which percolates upwardly through the slurry causing the bitumen to separate. The bitumen is collected at the top of the cavity and then is piped out. The invention disclosed in Yildirim requires that gas be injected into the cavity for purposes of maintaining a sufficient pressure within the cavity to prevent the overburden from collapsing.
Due to the problems associated with surface mining and in-situ mining techniques, hydraulic mining methods have been proposed as alternatives. Typically, hydraulic methods inserting an apparatus having nozzles into a borehole that has been drilled through an overburden to a tar sand formation and injecting jets of water into the sand formation. As in the in-situ methods, the water jets are injected into the formation thereby creating a slurry material to form in the cavity. The slurry material is then transported by pipeline to the surface for processing and removal of the bitumen. Once the bitumen is removed from the slurry and once the mining site is exhausted the sand and other material may be returned to fill in the resulting cavity to prevent subsidence. Hydraulic methods of mining also typically utilize gas to maintain sufficient pressure within the cavity during the mining operation to avoid subsidence problems.
The method disclosed in U.S. Pat. No. 5,249,844 issued to Gronseth (hereinafter referred to as "Gronseth") is typical of hydraulic methods of mining. Gronseth discloses a hydraulic method of mining that requires the drilling of a borehole into a tar sand reservoir. A casing is inserted within the borehole that extends through the overburden. A tubing with a water nozzle at its end is inserted into the borehole. Water is caused to flow through the tubing where it is emitted radially from nozzles. The emitted water causes the erosion of the tar sand formation, causing the sand particles and heavy oil to create a slurry. The resulting slurry is caused to flow upwardly through a second tubing to the surface for processing. After the cavity has been mined to its limit and the bitumen has been removed from the slurry, the oil depleted sand material is returned to he cavity.
However, existing hydraulic methods have many disadvantages similar to those of in-situ methods. For example, hydraulic methods suffer from the same inefficiencies associated with heating the fluid and using chemical additives. Hydraulic methods are also inefficient since the slurry material is pumped twice; once to the surface for processing and again back into the cavity when the mining in that cavity is completed. Hydraulic methods also require additional facilities to store slurry material while the cavity is being mined and while the bitumen is being separated. These inefficiencies make hydraulic mining not only more time consuming but more costly as well.
Also, most hydraulic and in-situ methods rely heavily on high pressure water jets to erode the tar sand formation to separate the bitumen. As those in the art can appreciate, as the tar sand formation is eroded and the distance from the water jets is increased, there is a significant decrease in force associated with the jets of water. Problems of water jet force are compounded as the mining cavity is filled with water. If the jets of water travel through a water medium the jet force is continuously reduced.
There have been attempts to overcome this problem. For example, in U.S. Pat. No. 4,437,706 issued to Johnson (hereinafter referred to as "Johnson") there is disclosed a method of mining that introduces high velocity jets of water into a cavity formation for purposes of causing the tar sand material to erode and cause the bitumen to separate from the tar sand. The apparatus in Johnson attaches the jet nozzles to a flexible tube that can be configured into various positions to produce a well or cavity of desired proportions. However, the primary purpose for the flexible tube is that it provides a method of keeping the jets in a very close proximate relationship to the formation so that the force of the jet of water on the formation can be maintained.
However, as those in the art can appreciate, this design has many disadvantages namely it is difficult, if not practically impossible, to configure and flex the tube once it is in a formation. The only way to reconfigure the tube is to stop the mining operation and withdraw the tube from the cavity in order to make the desired adjustment. This method is difficult to implement and inefficient.
There is a need for an hydraulic mining apparatus and method to overcome the limitations and inefficiencies in the prior art. Specifically, there is a need for an apparatus and method that provides a more cost effective and efficient erosion process. An apparatus and method is needed that does not rely solely on jets of heated fluid and chemical additives to cause erosion of the tar sand and separation of the bitumen.
3. Objects of the Invention
It is therefore an object of the present invention to provide a hydraulic mining apparatus and process which is simple in design and manufacture.
It is a further object of the present invention to provide an apparatus and process for hydraulically mining tar sand deposits and recovering the bitumen therefrom in an efficient and economic manner.
It is a further object of the present invention to provide an apparatus and process for hydraulically mining bitumen from tar sand formations that utilizes aggregate added to the deposit being mined as a scouring agent thereby permitting the efficient use of high pressure water and thermal energy for mining tar sand formations.
It is a further object of the present invention to provide for an apparatus and process for hydraulically mining bitumen from tar sand formations that will allow one formation to be mined while simultaneously reclaiming a second formation with bitumen depleted sand.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the invention without undue experimentation. The objects and advantages of the invention may be realized and obtained by means of the apparatus, methods and combinations as particularly pointed out in the appended claims.